CalPiByMutilThread.cpp

#include <iostream>
#include <windows.h>

CRITICAL_SECTION cs;

using namespace std;
static long num_steps = 1000000;
double step, pi;

double sum = 0.0;

DWORD WINAPI calSum(LPVOID p) {
	int *tmp = (int*)p;

	EnterCriticalSection(&cs);

	double x;
	for (int i = *tmp; i < num_steps; i += 4) {
		x = (i + 0.5) * step;
		sum = sum + 4.0 / (1.0 + x * x);
	}

	LeaveCriticalSection(&cs);
	return 0;
}

int main()
{
	int param[4];
	HANDLE hThreads[4];

	InitializeCriticalSection(&cs);

	step = 1.0 / (double)num_steps;
	for (int i = 0; i < 4; i++)
	{
		param[i] = i;
		hThreads[i] = CreateThread(0,0,calSum,&param[i],0,0);
	}

	WaitForMultipleObjects(4,hThreads,TRUE,INFINITE);
	DeleteCriticalSection(&cs);
	pi = step * sum;
	printf("Pi = % f\n", pi);
}